The present description relates to an internal combustion engine having homogeneous charge compression ignition (HCCI) combustion, and more particularly to a HCCI engine with a supercharger and direct fuel injection.
There is known, and, for example, described in Japanese patent application publication no. 2002-276442A2, a spark assisted HCCI combustion process. The Japanese publication discloses a method comprising the steps of injecting first stage fuel from an intake stroke to an early compression stroke of a cylinder cycle, igniting the first stage fuel by a spark to start first stage combustion, injecting second stage fuel, combusting a part of the second stage fuel by continuing the first stage combustion of the first stage fuel, and igniting the remaining part of the second stage fuel using greater heat and higher temperature created by the earlier combustion to make the second stage combustion.
The prior method can reliably control self ignition timing since the first stage combustion is started by the spark ignition to actively control the temperature in the combustion chamber. However, the spark assisted HCCI combustion may not have some of advantages the HCCI combustion can inherently have. Specifically, for the spark ignition of the first stage fuel, it needs to have a relatively fuel rich mixture around the spark plug. This means a greater amount of fuel is consumed, which deteriorates operating efficiency. Also, the fuel rich mixture may create more heat for a longer period of the spark ignited combustion than the HCCI combustion. The longer, hotter condition may create more nitrogen oxide, which deteriorates emission control performance.
Therefore, there is room for improvement of operating efficiency and emission control performance of HCCI engines while reliably controlling self ignition timing.